Non-invasive and repetitive imaging of a single cell or groups of cells in a living subject is crucial for in vivo tracking of cells, particularly in the field of cell-based therapy. Different imaging modalities have been used for understanding normal physiology and disease progression in many applications including cell-based therapies, cell trafficking, or gene therapy studies. Expression vectors having reporter nucleic acid sequences offer possibilities for non-invasive quantitative imaging of gene expression in living subjects.
To unravel the complexity and dynamics of molecular and cellular events, it is desirable to image the reporter gene expression in individual cells with the help of a single or multiple reporter gene construct. An imaging reporter gene encodes a protein that is detectable by various non-invasive imaging techniques. Reporter gene expression may be imaged in living subjects using optical imaging, positron emission tomography (PET), single-photon emission computed tomography (SPECT), or magnetic resonance imaging (MRI) depending on the type of reporter gene.
Stem cell-based therapy has revealed considerable potential, especially in the field of regenerative medicine. One of the obstacles for stem cell-based therapy is the lack of efficient monitoring methods to track the employed stem cells. Monitoring the differentiation status of a stem cell is essential to determining therapeutic efficacy as well as potential for adverse effects such as tumorogenicity of the implanted stem cell. Endogenous gene expression in cell culture or in living subjects may be assessed by using transgenes containing endogenous promoter driven reporter gene. Assessment of pluripotency of implanted stem cells may enable prediction of future terratoma formation. Pluripotency marker related promoter driven reporter gene system may help detect the differentiation status of a stem cell.
To overcome the shortcomings of each modality, a multimodality approach may be useful, which detect a plurality of different reporter gene expression. Moreover, a robust method to monitor the stem cell activity using non-invasive reporter gene imaging technique in living animal is a highly desirable goal.